From the co-operative research on the mechanisms controlling the determination and differentiation of muscle lineage cells, the followings were concluded.1) Myogenin is critical for muscle cell differentiation from myoblasts to myotubes and for the maturation of muscle fibers. MRF4 is expressed rather intensively in residual myotubes of mutant embryos than in myotubes of wild type littermates. Majority of myogenin-/-myotubes degrade at late embryonic stage. Secondary myotubes are scarcely generated. However, some secondary myoblasts are seen at muscle forming regions.2) The gene cascade required for the induction of muscle lineage cells from animal caps by the addition of actibin, was analyzed and cis regulatory elements regulating the initiation of myf-5 gene expression in early xenopus embryos, was detected.3) FGF,Shh, BMP,HGF,and Wn't are involved in the induction of muscle cells in chick myotomes and limb buds and the ectopic expression of FGF in lateral mesoderm induces extra-limb.4) Expression pattern of proteins regulating the polymerization of actin during embryogenesis and cytokinasis, was analyzed and revealed the importance of phosphorilation of cofilin.5) A novel G-protein expressed in skeletal muscle cells was identified.6) All actin genes were isolated from ascidian and examined their expressions in early embryos. Interestingly, some actin genes begin to express prior to the initial expression of MyoD.